This invention relates to magnetic induction transmitters and sound systems, and more particularly, to portable magnetic induction transmitters and sound systems that use personal magnetic induction transmission transducers.
Monophonic magnetic induction sound systems have been known for some time and have been used for a variety of purposes. In a magnetic induction sound system, output from an audio source such as a microphone or radio receiver is provided to a magnetic induction transmitter, such as a transmitting loop. The transmitter transmits a signal to a magnetic induction pick-up coil, also known as a telephone coil or T-coil, using a fluctuating magnetic field. The signal is received by the pick-up coil and is transmitted to an amplifier or earphone in an ear piece. Magnetic induction pick-up coils have been used in hearing aid devices for some time and were originally used to enable the user to listen to a telephone by inductive pick-up of fluctuating magnetic fields generated by a telephone receiver rather than by using a microphone in the hearing aid. Monophonic magnetic induction sound systems have also been used in classrooms. For example, transmitters, in the form of one or more large loops encircling a classroom or other larger area, have been used to transmit a signal to pick-up coils in ear pieces or hearing aids worn by users in an area encircled by or near the loop or loops. Similarly, individual monophonic magnetic induction sound systems have been disclosed in which a magnetic induction transmitter worn by a user transmits a monophonic signal to one or more pick-up coils worn by a user. A magnetic induction transmitter used in such an individual sound system has typically taken the form of a wire loop draped loosely around the neck of a user, with electricity passing through the loop to generate a fluctuating magnetic field that encircles the head of a user. Alternatively, it has been proposed to attach the magnetic induction transmitter directly to the outer casing of the ear piece. Monophonic magnetic induction sound system have been very beneficial, particularly for use by the hearing impaired, but the sound quality of the systems has been relatively poor.
In the field of high fidelity sound systems, stereophonic headphones have gotten smaller, and "wireless" headphones have been introduced. Nonetheless, headphones or ear pieces still typically require wires to be connected to the ear pieces to transmit the stereophonic signals. Even so-called "wireless" headphones typically use a relatively bulky headset having an external antenna that is hardwired to the ear pieces or ear phones that are secured to the headsets. These wireless headphones typically utilize radio or infrared signals broadcast by a near-by transmitter. Although typical stereophonic headphones provide good sound quality, it is sometimes undesirable to have wires extending between ear pieces and an audio source. Similarly, it is sometimes undesirable to wear bulky headphones. Particularly when engaging in physical activity, it is often difficult to retain such headphones or ear pieces in place. Also, prolonged use of such headphones or ear pieces is typically uncomfortable.